Marine vessels have a wide variety uses for transportation of people and cargo across bodies of water. These uses include fishing, military and recreational activities. Marine vessels may move on the water surface as surface ships do, as well as move beneath the water surface, as submarines do. Some marine vessels use propulsion and control systems.
Various forms of propulsion have been used to propel marine vessels over or through the water. One type of propulsion system comprises a prime mover, such as an engine or a turbine, which converts energy into a rotation that is transferred to one or more propellers having blades in contact with the surrounding water. The rotational energy in a propeller is transferred by contoured surfaces of the propeller blades into a force or “thrust” which propels the marine vessel. As the propeller blades push water in one direction, thrust and vessel motion are generated in the opposite direction. Many shapes and geometries for propeller-type propulsion systems are known.
Other marine vessel propulsion systems utilize water jet propulsion to achieve similar results. Such devices include a pump, a water intake or suction port and an exit or discharge port, which generate a water jet stream that propels the marine vessel. The water jet stream may be deflected using a “deflector” to provide marine vessel control by redirecting some water jet stream thrust in a suitable direction and in a suitable amount.
In some applications, such as in ferries, military water craft, and leisure craft, it has been found that propulsion using water jets is especially useful. In some instances, water jet propulsion can provide a high degree of maneuverability when used in conjunction with marine vessel controls that are specially-designed for use with water jet propulsion systems.
It is sometimes more convenient and efficient to construct a marine vessel propulsion system such that the net thrust generated by the propulsion system is always in the forward direction. The “forward” direction, or “ahead” direction is along a vector pointing from the stern, or aft end of the vessel, to its bow, or front end of the vessel. By contrast, the “reverse”, “astern” or “backing” directing is along a vector pointing in the opposite direction (or 180° away) from the forward direction. The axis defined by a straight line connecting a vessel's bow to its stem is referred to herein as the “major axis” of the vessel. A vessel has only one major axis. Any axis perpendicular to the major axis is referred to herein as a “minor axis.” A vessel has a plurality of minor axes, lying in a plane perpendicular to the major axis. Some marine vessels have propulsion systems which primarily provide thrust only along the vessel's major axis, in the forward or backward directions. Other thrust directions, along the minor axes, are generated with awkward or inefficient auxiliary control surfaces, rudders, planes, deflectors, etc. Rather than reversing the direction of a ship's propeller or water jet streams, it may be advantageous to have the propulsion system remain engaged in the forward direction while providing other mechanisms for redirecting the water flow to provide the desired maneuvers.
One example of a device that redirects or deflects a water jet stream is a conventional “reversing bucket,” found on many water jet propulsion marine vessels. A reversing bucket deflects water, and is hence also referred to herein as a “reversing deflector.” The reversing deflector generally comprises a deflector that is contoured to at least partially reverse a component of the flow direction of the water jet stream from its original direction to an opposite direction. The reversing deflector is selectively placed in the water jet stream (sometimes in only a portion of the water jet stream) and acts to generate a backing thrust, or force in the backing direction.
A reversing deflector may thus be partially deployed, placing it only partially in the water jet stream, to generate a variable amount of backing thrust. By so controlling the reversing deflector and the water jet stream, an operator of a marine vessel may control the forward and backwards direction and speed of the vessel.
A requirement for safe and useful operation of marine vessels is the ability to steer the vessel from side to side. Some systems, commonly used with propeller-driven vessels, employ “rudders” for this purpose. A rudder is generally a planar water deflector or control surface, placed vertically into the water, and parallel to a direction of motion, such that left-to-right deflection of the rudder, and a corresponding deflection of a flow of water over the rudder, provides steering for the marine vessel.
Other systems for steering marine vessels, commonly used in water jet stream propelled vessels, rotate the exit or discharge nozzle of the water jet stream from one side to another. Such a nozzle is sometimes referred to as a “steering nozzle.” Hydraulic actuators may be used to rotate an articulated steering nozzle so that the aft end of the marine vessel experiences a sideways thrust in addition to any forward or backing force of the water jet stream. The reaction of the marine vessel to the side-to-side movement of the steering nozzle will be in accordance with the laws of motion and conservation of momentum principles, and will depend on the dynamics of the marine vessel design.
Despite the proliferation of the above-mentioned systems, some maneuvers remain difficult to perform in a marine vessel. These include “trimming” the vessel, docking and other maneuvers in which vertical and lateral forces are provided.
It should be understood that while particular control surfaces are primarily designed to provide force or motion in a particular direction, these surfaces often also provide forces in other directions as well. For example, a reversing deflector, which is primarily intended to develop thrust in the backing direction, generally develops some component of thrust or force in another direction such as along a minor axis of the vessel. One reason for this, in the case of reversing deflectors, is that, to completely reverse the flow of water from the water jet stream, (i.e., reversing the water jet stream by 180°) would generally send the deflected water towards the aft surface of the vessel's hull, sometimes known as the transom. If this were to happen, little or no backing thrust would be developed, as the intended thrust in the backing direction developed by the reversing deflector would be counteracted by a corresponding forward thrust resulting from the collision of the deflected water with the rear of the vessel or its transom. Hence, reversing deflectors often redirect the water jet stream in a direction that is at an angle which allows for development of backing thrust, but at the same time flows around or beneath the hull of the marine vessel. In fact, sometimes it is possible that a reversing deflector delivers the deflected water stream in a direction which is greater than 45° (but less than 90°) from the forward direction.
Nonetheless, those skilled in the art appreciate that certain control surfaces and control and steering devices such as reversing deflectors have a primary purpose to develop force or thrust along a particular axis. In the case of a reversing deflector, it is the backing direction in which thrust is desired.
Similarly, a rudder is intended to develop force primarily in a side-to-side or athwart ships direction, even if collateral forces are developed in other directions. Thus, net force should be viewed as a vector sum process, where net or resultant force is generally the goal, and other smaller components thereof may be generated in other directions at the same time.
One particular aspect of marine vessel control which is lacking in some water jet propulsion systems is the availability to provide adequate trim or trimming force. “Trimming” force is a force that is substantially along the vertical axis of the vessel. This force acts to raise or lower the marine vessel, or parts thereof, along a vertical axis. Upwards trim force is developed by deflecting water from a water jet stream in a downward direction, and conversely, downward trim is developed by deflecting at least a portion of the water jet stream upwards. The various directions and axes described herein will be illustrated in more detail in the Detailed Description section below.
Steering and trimming control surfaces generally do not develop any backing thrust. Steering and trimming surfaces, such as rudders, trim tabs and interceptors provide forces along minor axes of a marine vessel and generally do not redirect any appreciable portion of a water jet stream in a direction less than 90° from the forward direction. Thus, these trimming and steering surfaces do not develop any significant backing thrust. Accordingly, steering and trimming control surfaces should not be confused with a reversing deflector, as reversing deflectors do provide a deflection of a water jet stream with enough forward deflection (having a component traveling in a direction less than 90° from the forward direction) to provide backing thrust.
In some cases it is advantageous to provide trim forces, especially at or near the aft end of a surface vessel, to achieve more efficient motion through the water. Some vessels, such as high-speed military and leisure craft, benefit from being able to ride “up on plane” with the trim of the vessel set at an angle to minimize resistance. The vessel may be made to rest or travel with varying inclination of its major axis. That is, the vessel's bow may be raised with respect to its stern.
Another reason that makes it desirable to be able to provide trim forces is to provide “active ride control.” By active ride control it is meant the ability to deliver varying amounts of trimming force to counter external variable forces on the marine vessel and make the vessel travel smoothly through the water. Passenger vessels, e.g., ferries, can benefit from a system that is able to counter excessive rocking and pitching due to rough seas. Control surfaces that can provide trimming forces could be used to counteract, pitch, roll and heave in real time to provide a more comfortable ride for a ship's occupants and cargo.
Furthermore, there is a need for control devices which can accurately control such trim deflectors and other control apparatus in marine vessels and other hydraulic control systems. Most conventional marine vessel control systems comprise purely mechanical devices, which convert some input from a marine vessel operator into a force or a deflection motion of a control surface. For example, when the vessel operator moves a control lever handle, the control lever handle typically either directly moves a rudder through a linkage, or controls a position of a hydraulic valve which then causes the control surface to move due to hydraulic fluid pressure on an actuator of the control surface.
Hydraulic power assistance for actuating the steering nozzles and reversing deflectors is especially useful or necessary for large vessels at high speeds where large forces are needed to resist the water forces and mechanical forces acting on the control surfaces.
Some marine vessel control systems that use hydraulic fluid pressure to actuate various actuators of the control systems suffer from weaknesses that reduce the effectiveness of these control systems. This can jeopardize the safety of the marine vessel and its operators. For example, many current hydraulic control systems experience high-pressure transients which propagate through the hydraulic system and affect the operation and safety of the system in an undesirable way. These transients, sometimes known as “kickback”, are a result of fluid trapped in hydraulic components following a hard-steering evolution. Hydraulic fluid-high pressure transients can also adversely affect the longevity of the components within the system, as well as cause hazards to the operators of the system, to the marine vessel and to its cargo.